History of Car Brakes: From Wooden Blocks to ABS

Why were the first brakes pressed against the wheel rim?

Horse-drawn wagons and early carriages slowed down with a lever that pushed a block of wood or leather against the outside of the wheel. It was simple, and at walking pace it worked. The problem showed up when vehicles got faster and heavier. A block on an exposed rim wears quickly and works poorly when it is wet or muddy.

Early motor cars borrowed the idea, with brakes acting on the transmission or on the outside of the wheels. They soon needed something that could handle more speed and keep dirt and water away from the friction surfaces.

What did hydraulic brakes change?

The answer to the dirt problem was the drum brake, which places the friction parts inside a metal drum so they are shielded from the weather. Louis Renault is commonly credited with an early drum brake design in the early 1900s.

Early drum systems still relied on rods and cables to carry the driver's foot force to each wheel. Those linkages stretched, needed constant adjustment, and made it hard to apply equal force at every wheel. Hydraulics solved that by using fluid, which cannot be compressed in any useful way, to send pressure through lines to each wheel at once.

Hydraulic brakes were developed over the 1910s and 1920s, and Duesenberg is widely cited as an early maker to fit them on a production passenger car in the early 1920s.

When did disc brakes win out over drums?

Drums have a weakness: they trap heat. When a drum gets very hot, the brake can fade and lose stopping power. Frederick Lanchester patented a disc brake design in the early 1900s, but materials and manufacturing were not ready to make it practical for years.

A disc is open to the air, sheds heat more easily and recovers more predictably, and it handles water better. Racing proved the point in the 1950s, when Jaguar used Dunlop disc brakes on its cars at the 24 Hours of Le Mans, and road cars adopted them in the years that followed, usually at the front first, where most of the braking work is done.

Many cars still use drums at the rear today, because they work well for lighter loads and are well suited to a parking brake mechanism.

What did ABS add that stronger brakes could not?

Strong brakes bring a different problem. If the driver brakes hard enough to lock a wheel, the tire skids, the car loses steering control, and a locked tire is often not stopping as well as one that is still rolling.

Anti-lock braking systems use wheel-speed sensors and a hydraulic control unit that rapidly releases and reapplies pressure at a wheel that is about to lock. The driver keeps steering control while braking hard. Electronic anti-lock systems reached series-production cars in the late 1970s, with Mercedes-Benz and Bosch among the best-known early names.

Those same sensors and valves became the foundation for traction control and electronic stability control, which can brake individual wheels to help keep the car on its intended path. The story keeps going, and the problem is still the same one: slowing a moving mass, safely, in every kind of weather.